leetcode 264. Ugly Number II

最新推荐文章于 2024-06-04 11:57:06 发布

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最新推荐文章于 2024-06-04 11:57:06 发布

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本文介绍了一种使用动态规划方法来寻找第N个丑数的高效算法。丑数定义为仅包含质因数2、3和5的正整数。文章通过一个具体的Java代码示例展示了如何实现这一算法。

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Write a program to find the n-th ugly number.

Ugly numbers are positive numbers whose prime factors only include 2, 3, 5. For example, 1, 2, 3, 4, 5, 6, 8, 9, 10, 12 is the sequence of the first 10 ugly numbers.

Note that 1 is typically treated as an ugly number, and n does not exceed 1690.

每次筛选出下一个ugly数，运用DP

public class Solution {
    public int nthUglyNumber(int n) {
        int[] ugly = new int[n];
        ugly[0] = 1;
        int fact2 = 2, fact3 = 3, fact5 = 5;
        int index2 = 0, index3 = 0, index5 = 0;
        for(int i=1; i<n; i++){
            int min = Math.min(Math.min(fact2, fact3), fact5);
            ugly[i] = min;
            if(min==fact2) fact2 = 2*ugly[++index2];
            if(min==fact3) fact3 = 3*ugly[++index3];
            if(min==fact5) fact5 = 5*ugly[++index5];
        }
        return ugly[n-1];
    }
}